I. Field of the Invention
The present invention relates to the field of turbo-engines, in particular an improved bladed stator for a turbo-engine.
II. Description of Related Art
An aeronautical turbo-engine conventionally comprises a compressor, a combustion chamber and a turbine. The role of the turbine is to provide the rotary drive of the compressor by taking part of the pressure energy of the hot gases leaving the combustion chamber and converting it into mechanical energy.
The turbine, located downstream of the combustion chamber, is the element of the turbo-engine which works in the severest conditions. In particular, it is subjected to great thermal and mechanical stresses generated by the hot gases leaving the chamber.
An axial turbine conventionally comprises at least one stator, consisting of a row of blades which are fixed in relation to the housing of the turbo-engine, and at least one rotor disk, comprising a set of blades which is capable of being set in rotation.
The stator blades are in general fixed radially in relation to the axis of rotation of the turbo-engine on two concentric annular shrouds, referred to as the inner shroud and the outer shroud, one end of the blades being connected to the inner shroud and another end of the blades being connected to the outer shroud.
The stator can be divided into sectors, each sector being provided with a plurality of blades. On a turbo-engine, the stator sectors are fixed to a fixed annular housing. Mounting a plurality of identical sectors connected end to end in a ring on a fixed annular housing makes it possible to reconstitute the stator. The stator sectors comprise an axis of revolution which is coaxial with the axis of rotation of the turbo-engine.
On a stator sector, the inner shroud and outer shroud portions are respectively called the inner platform and the outer platform. The space defined between the inner platform and the outer platform constitutes an air stream in which air originating from the combustion chamber flows.
The platforms comprise parts exposed directly to the air stream and other, non-exposed parts. Consequently, the parts exposed to the hot gases, such as the surfaces delimiting the air stream, will expand more rapidly than the non-exposed parts, such as flanges described in detail below.
Furthermore, the platforms are more solid pieces than the blades. Therefore, the platforms have a greater thermal inertia than the blades, which has two consequences: under the effect of an increase in temperature, on the one hand the blades will expand more rapidly than the platforms, and on the other hand the platforms will impose their deformation on the blades. This phenomenon is also called the bimetallic effect.
During the various phases of flight of an aircraft equipped with a turbo-engine, the stator undergoes heating and cooling, which deforms the inner and outer platforms. Under the effect of these deformations, the blades of the stator are subjected to a succession of traction and compression, and this leads to the appearance of cracks which are detrimental to the lifetime of the blades.
To solve these problems, a solution known from the prior art consists in designing stator sectors with platforms which are not very solid. However, this solution is far from satisfactory because the mechanical behavior of such stator sectors is affected by it.